1. Field of the Invention
The present invention relates to a portable internal combustion-engined tool and a method of forming a gas mixture in the tool combustion chamber. In particular, the present invention relates to a setting tool for driving-in fastening elements.
2. Description of the Prior Art
A tool and a method, which are referred to above, are described in a German Publication No. 199 50 352. In the tool, the combustion chamber can be brought into a collapsible condition when chamber walls provided therein and limiting chamber sections are displaced in a direction toward the chamber bottom and lie one upon another, whereby an expandable space is formed in the combustion chamber which is located, in a direction of displacement of the limiting walls, behind the last displaceable wall.
The tool described in the German publication includes a piston having a piston plate, and a combustion chamber for generating power for driving the piston and having a bottom adapted to receive the piston plate, an end wall located opposite the bottom, a movable wall located between the bottom and the end wall and provided with a check valve, a movable separation wall located between the bottom and the movable wall and provided with a plurality of openings, with the movable wall and the separation wall being displaceable in a direction of the bottom upon collapsing of the combustion chamber. In the side wall of the combustion chamber, there is provided means for feeding fuel gas thereinto.
The fuel gas is fed during the expansion of the chamber sections and actually shortly before they reach their completely expanded condition. Immediately thereafter, ignition takes place. As a result, the fed fuel gas has little time for homogeneous or uniform distribution in the combustion chamber. When the fuel gas is fed in a liquified state, a danger exists that the fuel gas would not evaporate completely. In both cases, the operating efficiency of the tool is reduced.
Accordingly, an object of the present invention is to provide a tool and a method which would insure a homogeneous distribution of the fuel gas in the combustion chamber.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by feeding fuel gas into the expandable space which is formed behind the movable wall when the movable wall is displaced in the direction toward the chamber bottom.
The fuel gas can be fed into the expandable space shortly after the combustion chamber starts to collapse, when the expandable space has not yet expanded completely, or upon the complete expansion of the expandable space.
According to a preferred embodiment of the present invention, a check valve is provided in the end wall of the combustion chamber for admitting fresh air thereinto. The fresh air is aspirated into the expandable space upon collapsing of the combustion chamber. The check valve in the end wall at the same time prevents leakage of the fuel gas outside.
The fuel gas can be injected in a liquified form, gaseous form, or an already available air-fuel gas mixture can be injected.
In the collapsible condition of the combustion chamber, in the rear portion of the chamber, i.e., in the expandable space, a fresh air is present. Simultaneously or shortly after the tool has been pressed against an object, in which a fastening element has to be driven in, the fuel gas is injected into the expandable space, and the chamber sections begin to expand as a result of displacement of the movable walls. The fuel gas is mixed with air only in the rear space and flows into the respective chamber sections through openings provided in the movable walls. At that, the gas flow is deflected to provide for a better intermixing of the air-fuel gas mixture. Upon the complete expansion of the chamber sections and the reduction of the rear space practically to zero, the entire air-fuel gas mixture is available in the combustion chamber section and, thus, can be ignited. As a result of good or homogeneous intermixing of the air-fuel gas mixture, the combustion is characterized by a high efficiency which leads to a high energy release. When a liquified fuel gas in injected, there is sufficient time available for its evaporation as the ignition does not take place shortly after the injection but only after the complete expansion of the chamber sections. This further contributes to the increased efficiency of the tool.
According to a preferred embodiment of the present invention, as discussed above, a check valve is provided in the combustion chamber end wall, so that a fresh air is always aspirated into the combustion chamber as it collapses.
When the combustion chamber collapses, the residual gases are expelled through a check valve provided in the combustion chamber bottom. A still further check valve is provided in the combustion chamber movable wall, which faces the stationary end wall. This check valve provides for flow of the air-fuel gas mixture from the rear space into the expandable chamber sections but prevents flow of the residual gases from the chamber sections into the rear space.
According to further development of the present invention, the separation wall has an upwardly extending lug provided at its free end with a shoulder. The movable wall has a hollow extension which surrounds the lug of the separation wall. Both the separation wall lug and the movable wall extension extend through the end plate. A seal is provided between the movable wall extension and the wall of the opening in the end wall, through which the lug and the extension extend, in order to prevent any leakage of the air-fuel gas mixture. The movable wall extension and the separation wall lug are provided to insure displacement of the separation wall upon displacement of the movable wall. The distance between the end surface of the extension and the lug shoulder defines the distance between the movable wall and the separation wall and thereby the size of the forechamber section.
The fuel gas feeding means can be connected with a single metering valve. The metering valve can be set for a large amount which improves the metering precision. A standard valve can be used as a metering valve, which reduces the cost of the tool. The metering valve can be connected with the combustion chamber by one or several feeding channels or conduits.
Means is provided to insure the injection of the fuel gas at the beginning of the setting process to provide sufficient time for the liquified gas to evaporate. Eventually, an electronic control can be used to prevent ignition before expiration of certain time.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood form the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.